This application relates generally to guided missiles and more particularly to improving the effectiveness of missiles fired at airborne targets.
Guided missiles fired at airborne targets are well known. Certain types of such missiles contain a radar fuzing system. The fuzing system detects the presence of a target and measures the range between the missile and the target. At an appropriate range, the fuzing system detonates a warhead. The explosion of the warhead propels a cloud of shrapnel in all directions relative to the missile. If enough of the shrapnel strikes the target at a vulnerable area, the target is destroyed.
The fuzing system of one existing missile comprises two transmit antennas and two receive antennas. Each transmit antenna radiates a radar signal modulated with a pseudo noise (hereafter PN) sequence into a roughly 180.degree. sector relative to the missile. Each receive antenna receives radar reflections from a 180.degree. sector. Both transmit antennas are fed the same signal. Likewise, both received signals are combined. Thus, the four antennas provide 360.degree. coverage to both transmit and receive signals.
The received signal is mixed with several copies of the PN sequence, each delayed by a different time. Mathematically, this mixing correlates the received signal with the transmitted signal. The time delay associated with the delayed copy of the PN signal which produces the highest correlation indicates the back and forth propagation time to the target and, hence, indicates the range to the target. The measured range indicates when the fuzing system should detonate the warhead.
To avoid detonating the warhead when no target is present, the warhead is not detonated unless the highest correlation signal exceeds a threshold. The threshold is determined by correlating the PN signal with the background noise signal present when a reflected radar signal is not being received. This threshold signal gives a measure of the background noise level. Accordingly, the warhead is not detonated unless the highest correlation signal is above the noise.
While this arrangement for detonating a warhead is adequate for some applications, it is desirable to improve the effectiveness of the missile for other applications.
One way to improve the effectiveness of a missile is to direct the energy from the detonation of the warhead towards the target. Directional warheads are known that contain directing charges. In some systems, called mass focus systems, the directing charge deforms the shell of the missile. When the main explosive charge of the warhead explodes, the shrapnel tends to be focused towards the deformed region. In other systems, called velocity focus systems, a directing charge is detonated and creates a shock wave in a particular direction. The explosion of the main explosive charge while the shock wave is present causes shrapnel in the direction of the shock wave to have a greater velocity.
Regardless of which type of directional warhead is used, it is necessary for the fuze detonating the warhead to determine the direction of the target relative to the missile. Additionally, it would be desirable to create a directional warhead system with as little change as possible to an existing fuzing system.